1998 Ford Expedition Repair Question
Engine light staying on after
Asked by redrooster275Answer
Fault codes never say to replace parts. If it was that simple, we wouldn't need mechanics. They only indicate the circuit or system that needs further diagnosis. There can be a corroded connector terminal, bare wire, emissions passage plugged with carbon, and lots of other causes for a code other than a bad sensor.
The white smoke indicates burning coolant. If the coolant level has been dropping in the reservoir, suspect a leaking head gasket. If the level is fine, you might be seeing normal condensation burning off when you start the engine. Regardless, the cause for the misfire should be diagnosed first. I suspect the codes you're getting are from the sensors reporting the results of that misfire, not causing them.
like i said i dont know much about cars. Im kinda illiterate about them. I just dont want to get taken advantage again. If im replacing these parts an it shows back up on a diagnosis whats the deal and what do i do next. Check the plugs, coil what, idk. i appreciate your info.
The codes indicate the circuit that needs to be diagnosed. After the diagnosis is when a part is replaced if that's what's needed. You're replacing parts before the cause of the problem is diagnosed. That's the most expensive and least effective way to fix a problem.
The oxygen sensor codes could mean that side of the engine is running lean. You don't replace the sensor just because you don't like the problem it reported. One thing to keep in mind is when you have a misfire it is due to loss of fuel, loss of spark, or loss of compression meaning an engine problem. The most common cause is loss of spark. That means unburned fuel and air go into the exhaust system where the oxygen sensor detects the unburned oxygen. You might smell the unburned fuel at the tail pipe but oxygen sensors don't detect fuel, just oxygen. Depending on the strategy of the Engine Computer, it might command more fuel to that side of the engine in response to thinking it's running lean. That will make your fuel mileage and engine performance even worse, and no matter how much extra fuel it adds, there will still always be that unburned oxygen getting detected.
Another common problem that only occurs on Ford trucks is a plugged EGR emissions tube. The passages become plugged with carbon. If the passage to one cylinder is plugged, only fresh air and fuel will go into that cylinder and it will be fine. As more and more passages to different cylinders become plugged, pretty soon all the exhaust gas is routed to the one remaining cylinder where its passage isn't plugged yet, and since there's so much exhaust gas going into it, there's no room for fresh air so that cylinder misfires. As far as the EGR tubes are concerned, the one going to the misfiring cylinder is the only one that isn't plugged.
Those are just a couple of examples of what can happen. As I mentioned previously, wiring problems are just as common as sensor problems. A bad sensor will be the cause of setting a fault code only about half of the time. Their purpose is to monitor specific aspects of the engine, and when they set a code because something is wrong with the way the engine is running, they're doing their job. Replacing them isn't going to help.
okay, heres the newest. I ended up having a cracked head. dealer replaced it. Now engine light stayed on. I took back and they replaced a 02 sensor and cleaned my egr port. Light went off but truck still is missing when im at a idle or in park. Like it wants to stall. I still think egr valve. but i dont know. Do I take it back to them with this issue or what else can it be.
Absolutely take it back. They deserve the chance to check their work and correct any mistakes. There can also be other additional defective parts that didn't show up previously. Spark plugs are good for that but that's just one example. Depending on what they find, if a new part is bad or if they did something wrong, you should not be charged, but if some other part is bad it is perfectly legitimate to expect you to pay for it, but very often they will not charge you for the diagnosis and / or labor. There's nothing unethical about charging you for the labor if they didn't do anything wrong last time, after all, no one else works for free, but in the spirit of customer goodwill, and as a way of apologizing that you had to come back so soon, they will often overlook additional labor charges. It depends on the marketing mentality of the shop. Some want to squeeze as many dollars out of you now because they know you're never coming back, (typical GM dealership), and some build customer loyalty by charging more fairly so you come back often, (typical Chrysler dealership). Ford is in the middle of those two extremes.